For me, evaluating my teaching used to be a subjective business. As the children left the room, I would say, ‘Well, I think that went rather well!’ or ‘Well, they seemed to enjoy it …’. If I had taught something, quite well in my opinion, to an apparently interested class, then my assumption was that they had learned it. This is still a common equation: decent teaching plus a reasonably co-operative class equals learning. When asking a question such as ‘Why are you sure they all understand right-angled triangles?’, I frequently receive the answer, ‘Because we did them last week’.